Fluctuations in optical bistable systems

The bistable behaviour of an ensemble of two level atoms driven by a coherent external light field is discussed in the adiabatic limit when the relaxation of the atoms is fast compared to the relaxation of the field. The influence of the different noise sources is discussed separately in a one-dimensional approximation by neglecting the phase fluctuations. In the case where the fluctuations of the driving field play the dominant role, an exact solution of the two-dimensional stationary Fokker-Planck equation is derived describing amplitude as well as phase fluctuations.